Note 2 - Revenue Recognition - Significant Changes in Contract Assets and Deferred Revenue (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Receivables	$ 6,177,000	$ 9,216,000
Short-term contract assets	456,000	494,000
Long-term contract assets		237,000
Short-term contract liabilities (deferred revenue)	2,165,000	1,559,000
Long-term contract liabilities (deferred revenue)	28,000	903,000
Revenue recognized that was included in the contract liability at beginning of the period	1,633	2,033
Transferred to receivables from contract assets outstanding at beginning of the period	$ 47	$ 302